It seems like you might have just entered "a" by accident or were starting a new question. If you have any further questions or need more details on the previous solution, feel free to ask!

Here are some options you might be considering:

1. Would you like more details on how the sum of the interior angles is calculated for polygons?
2. Do you have another geometry problem you'd like to solve?
3. Are you interested in exploring the properties of different types of polygons?
4. Do you need help with a different topic in mathematics?
5. Would you like a deeper explanation of how to approach problems involving angles in quadrilaterals?

Tip: If you're unsure about any step in a geometric proof or calculation, breaking it down into smaller parts can help clarify the reasoning process.